1. Field of the Invention
The present invention relates to electromagnetic coupling devices, and more particularly, to a system for dissipating heat from the inductor drum of such devices.
Electromagnetic couplings of the type well known in the art include a rotor which is disposed within a rotatable inductor drum. A coil is energized to generate a magnetic field which electromagnetically couples the rotor and drum so that torque may be transmitted therebetween. The passage of this magnetic field through the rotor and the inductor drum results in the generation of heat during the transmission of torque, partially as a result of "slip" between the rotor and the inductor drum (power in = power out + heat). The dissipation of this heat has long been a problem for those working in this art and different types of cooling systems have been tried in an effort to more effectively dissipate the generated heat. Generally, the heat buildup limits the power ratio of the coupling. Thus, by increasing the heat dissipation of a particular size coupling, the power ratio can be increased.
2. Prior Art
In many different embodiments of electromagnetic couplings, heat-dissipating fins have been provided which extend either radially or axially from the exterior of the inductor drum. However, such fins have not provided sufficient cooling of the coupling and, in addition, may create enough noise that a silencer is required. U.S. Pat. No. 2,345,850 illustrates an example of a typical fin cooling system.
In an effort to utilize the flow of cooling fluid more effectively, the device shown in U.S. Pat. No. 2,745,974 includes an inductor drum encircling the field pole output member. This output member comprises a series of circumferential, spaced magnetic poles excited by the field coil, the poles being formed of a ferromagnetic material. The inductor member includes a plurality of fins and permits air flow through the circumferential slots defined by adjacent magnetic poles, drawing air through the gap between the poles and the fins, then over the fins. One disadvantage of this arrangement is the interruption of eddy currents and the related magnetic reluctance caused by the circumferential cooling slots, thereby resulting in a reduced torque-transmitting capacity.
The device illustrated in U.S. Pat. No. 3,641,375, assigned to the assignee of the present invention, utilizes a series of pressurized chambers spaced circumferentially around the housing of the coupling. The cooling fluid (such as air) from these pressurized chambers impinges against the surface of the inductor drum, then passes to an adjacent exhaust pocket. While the cooling ability of this device was generally acceptable, it required a means for pressurizing the pressure chambers, such as a blower or fan. In addition, the arrangement of alternating pressure chambers, exhaust pockets and the associated baffles was difficult and expensive to manufacture and required excessive space within the housing of the coupling.